The present invention relates to a solid state image sensing device comprising a plurality of static induction transistors each constituting a pixel
Heretofore, there has been proposed, for instance Japanese Patent Application Laid-open Publication No. 105,672/83, a solid state image sensing device comprising pixels, each being formed by a static induction transistor (hereinafter abbreviated as SIT), serving as a photodetecting and switching element. Further, a linear or one dimensional solid state image sensing device comprising SITs has been proposed.
FIG. 1 is a cross section showing a single pixel of a known linear image sensing device comprising SITs serving as the photodetecting and switching elements. An SIT comprises an n.sup.+ substrate 1 constituting a drain, an n.sup.- epitaxial layer 2 serving as a channel region, a p.sup.+ gate diffusion region 3, a p.sup.+ shield gate diffusion region 4, an n.sup.+ source diffusion region 5, a source electrode 6 formed on the region 5, and a gate electrode 7 formed on the gate region 3 via a gate insulating film 8. Between the gate region 3 and gate electrode 7 is formed a capacitance. The source electrode 6 is connected to a signal readout line 10 in which a refresh selection switch 9 is connected. The shield gate region 4 is connected to a refresh transistor 11 via a reset line 12. The refresh selection switch 9 is further connected to a signal detecting section 13.
FIG. 2 is a circuit diagram illustrating a known one dimensional solid state imaging sensing device comprising the pixels shown in FIG. 1. The device comprises a plurality of SITs 20-1, 20-2 . . . 20-n arranged linearly, gates of SITs being connected to a scanning circuit 21 and sources of SITs being commonly connected to the signal readout line 10 which is connected via the refresh selection switch 9 to the signal detecting section 13 having a load resistor R.sub.L and a voltage supply source V.sub.V. The shield gates of the SITs 20-1, 20-2 . . . 20-n are commonly connected to the reset line 12 which is connected to the ground via the refresh transistor 11. The drains of the SITs are commonly connected to the ground.
FIGS. 3A to 3C are waveforms for explaining the operation of the known solid state image sensing device shown in FIG. 2. When the scanning circuit 21 applies signals .phi..sub.G1, .phi..sub.G2 . . . successively to the gates of successive SITs 20-1, 20-2 . . . as illustrated in FIGS. 3A and 3B, an output signal V.sub.out at the signal detecting section 13 changes as depicted in FIG. 3C. As can be understood from the waveform, during the readout period T.sub.O the gate potential of SIT is refreshed to a potential which is substantially equal to a built-in voltage .phi..sub.B of a pn junction between the p.sup.+ gate region 3 and the n.sup.- epitaxial layer 2, said potential being near zero volt. Therefore, in the known solid state image sensing device shown in FIG. 2, the refresh selection switch 9 is in fact unnecessary and further the refresh transistor 11 is used not to provide the refresh function, but to control overflow of the gate potential of SIT serving as the photodetecting element.
As explained above, in the known solid state image sensing device, since the SIT is refreshed by the driving signals .phi..sub.G1, .phi..sub.G2 . . . , it is impossible to effect a non-destructive readout of the light charge stored in the SIT. Therefore, in the known device it is impossible to effect a photometry for an light image during the image pick-up.